Various forms of drug delivery catheters are known in the art. They generally comprise an elongated flexible catheter body having an inflatable member at a distal end portion thereof where the inflatable member or "balloon" has pores formed in the wall thereof through which a drug containing fluid can profuse. For example, U.S. Pat. No. 5,709,653 to Leone uses a balloon catheter with a porous balloon for allowing a photodynamic treatment fluid to pass through the pores and infuse into the wall of a body vessel in which the catheter is disposed. Other patents utilizing a porous balloon for drug delivery include Racchini et al. U.S. Pat. No. 5,458,568; Sahatjian et al. U.S. Pat. No. 5,674,192 and Shapland et al. U.S. Pat. No. 5,628,730.
Unfortunately, porous balloons are difficult to manufacture (requiring precision drilling of an elastic material) and the minimum practical pore size is often much larger than desired. Moreover, the typical porous balloon system of the prior art has an undesirable release profile, characterized by rapid initial release of a drug or other agent followed by an exponential drop-off as the balloon deflates and the fluid pressure driving the agent through the pores becomes smaller and smaller.
Accordingly, there exists a need for better drug delivery systems and, in particular, delivery systems with greater control over release rates. Balloon or other membrane-based drug delivery systems that can selectively pass molecules at a controlled and reproducible rate would satisfy a long-felt need in the art.